Apparatus and method for mask free delivery of an inspired gas mixture and gas sampling

ABSTRACT

This disclosure is of a mask-free device for supplying sufficient gas to a medical patient and for more accurately sampling the exhalation gas of the patient. The device includes a flexible body having lumens adapted to extend into the nares of a patient and adjacent the patient&#39;s mouth for collecting and transmitting a sampling of the patient&#39;s end tidal exhalation to a gas analyzer to analyze one or more component gases in that exhalation. The disclosure also discloses the transmittal of pressure from the nares of the patient to a pressure transducer for determining the respiratory phase of the patient and for controlling the volume of oxygen delivered to the patient. The body of the mask-free unit further includes conduits for delivering oxygen through diffuser orifices to positions adjacent the patient&#39;s nares and mouth. Finally, a controller is interconnected between the pressure transducer and the gas supply for increasing the delivery of gas during the inhalation phase of the patient&#39;s respiration and for decreasing said delivery upon the exhalation phase for the purpose of avoiding dilution of the exhalation sample.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/878,922, filed Jun. 13, 2001, now U.S. Pat. No. 7,152,604, which is aContinuation-In-Part of U.S. patent application Ser. No. 09/592,943,filed Jun. 13, 2000 now U.S. Pat. No. 6,938,619, the contents of whichare incorporated herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an apparatus and method for the delivery of aninspired gas (e.g., supplemental oxygen (O₂) gas) to a person combinedwith sampling of the gas exhaled by the person, such sampling for use,for example, in monitoring the ventilation of the person or forinferring the concentration of a drug or gas in the person's bloodstream. More particularly, the invention relates to an apparatus andmethod where such delivery of the inspired gas and gas sampling areaccomplished without the use of a sealed face mask.

2. Description of Related Art

In various medical procedures and treatments performed on patients,there is a need to deliver a desired inspired gas composition, e.g.,supplemental oxygen, to the patient. In procedures involving thedelivery of anesthesia or where a patient is otherwise unconscious andventilated, the delivery of oxygen and gaseous or vaporized or nebulizeddrugs is typically accomplished via a mask that fits over the patient'snose and mouth and is sealed thereto or by a tracheal tube. In otherprocedures, however, for example, where a patient may be sedated, butconscious and breathing on their own, the delivery of supplementaloxygen or inspired gas may be accomplished via a mask or by nasalcannulae (tubes placed up each nare of a patient's nose), connected to asupply of oxygen or the desired gas composition.

Taking oxygen as one example of an inspired gas to be delivered to aperson, the primary goal of oxygen supplementation (whether mask-free orotherwise) is to enrich the oxygen concentration of the alveolar gas,namely, the mixture of gas in the alveoli (microscopically tiny clustersof air-filled sacs) in the lungs. In a person with normal lung function,the level of oxygen in the deepest portion of the alveolar sacs isessentially reflected at the end of each “tidal volume” of exhaled gas(the volume of gas in one complete exhalation). The gas sample measuredat the end of a person's exhalation is called the “end-tidal” gassample.

So, for example, if a person breathes room air, room air contains 21%oxygen. When the person exhales, the end tidal gas will have about 15%oxygen; the capillary blood has thus removed 6% of the oxygen from theinhaled gas in the alveoli, to be burned by the body in the process ofmetabolism. Again, a simple goal of any form of oxygen supplementationis to increase the concentration of oxygen in the alveolar sacs. Aconvenient method of directly measuring or sampling the gas in alveolarsacs is by continuously sampling the exhaled gas at the mouth or noseand identifying the concentration of oxygen at the end-tidal point, avalue that is reasonably reflective of the oxygen concentration in thealveolar sacs. Thus, one can compare the effectiveness of oxygendelivery systems by the amount that they increase the end tidal oxygenconcentration.

If a person breathes through a sealing face mask attached to one-wayvalves and inhales a supply of 100% oxygen, the end tidal concentrationof oxygen goes up to 90%. More specifically, once inert nitrogen gas hasbeen eliminated from the lungs (after pure oxygen has been breathed forseveral minutes), alveolar gas will contain about 4% water vapor and 5%carbon dioxide. The remainder (about 90%) will be oxygen. Thus, the bestoxygen delivery systems typically increase end tidal oxygen from abaseline of 15%, when breathing non-supplemented room air, to 90% whenbreathing pure oxygen. Although sealed face-masks are relativelyeffective oxygen delivery systems, conscious patients, even whensedated, often find masks significantly uncomfortable; masks inhibit theability of a patient to speak and cause anxiety in some patients.

Nasal cannulae, on the other hand, do not typically cause the level ofdiscomfort or anxiety in conscious patients that masks do, and thus,from a patient comfort standpoint, are preferable over masks for thedelivery of oxygen to conscious patients. Nasal cannulae are, however,significantly less effective oxygen delivery systems than sealed facemasks. Nasal cannulae generally increase the end tidal oxygenconcentration to about 40% (as compared to 90% for a sealed mask). Nasalcannulae are less effective for at least two reasons.

First, when a person inhales, they frequently breathe through both nasalpassages and the mouth (three orifices). Thus, the weighed averageconcentration of inhaled oxygen is substantially diluted to the extentof mouth breathing because 21% times the volume of air breathed throughthe mouth “weights down the weighted average.”

Second, even if a person breathes only through their nose, the rate ofinhalation significantly exceeds the supply rate of the nasal cannula(typically 2-5 liters/min.) so the person still dilutes the inhaledoxygen with a supply of 21% O₂ room air. If the nasal cannula is flowingat 2 liters per minute and a person is inhaling a liter of air over 2seconds, the inhalation rate is 30 liters per minute, and thus, most ofthe inhaled volume is not coming from the nasal cannula, but rather fromthe room. Increasing the oxygen flow rate does not effectively solvethis problem. First, patients generally find increased flow veryuncomfortable. Second, increased inspired gas flow dilutes (washes away)exhaled gases like carbon dioxide and/or exhaled vapors of intravenousanesthetics or other drugs. When this happens carbon dioxide cannot beaccurately sampled as a measure of respiratory sufficiency. Also, a drugsuch as an inhalational or intravenous anesthetic, cannot be accuratelysampled as a measure of the arterial concentration of the drug fromwhich, for example, the level of sedation might be inferred. There is aneed in various medical procedures and treatments to monitor patientphysiological conditions such as patient ventilation (the movement ofgas into and out of the lungs, typically measured as a volume of gas perminute). If the patient does not move air into and out of the lungs thenthe patient will develop oxygen deficiency (hypoxia), which if severeand progressive is a lethal condition. Noninvasive monitoring of hypoxiais now available via pulse oximetry. However, pulse oximetry may be lateto diagnose an impending problem because once the condition of low bloodoxygen is detected, the problem already exists. Hypoventilation isfrequently the cause of hypoxemia. When this is the case,hypoventilation can precede hypoxemia by several minutes. A good monitorof ventilation should be able to keep a patient “out of trouble” (if thecondition of hypoventilation is diagnosed early and corrected) whereas apulse oximeter often only diagnoses that a patient is now “in” trouble.This pulse oximetry delay compared to ventilatory monitoring isespecially important in acute settings where respiratory depressantdrugs are administered to the patient, as is usually the case duringpainful procedures performed under conscious sedation.

Ventilatory monitoring is typically measured in terms of the totalvolumetric flow into and out of a patient's lungs. One method ofeffective ventilatory monitoring is to count respiratory rate and thento measure one of the primary effects of ventilation (removing carbondioxide from the body). Certain methods of monitoring ventilationmeasure the “effect” of ventilation (pressure oscillations, gas flow,breath sound and exhaled humidity, heat or CO₂ at the airway). Otherventilation methods measure the “effort” of ventilation (e.g.,transthoracic impedance plethysmography, chest belts, respiratory rateextraction from optoplethysmograms). Effort-based ventilation monitorsmay be less desirable because they may fail to detect a blocked airwaywhere the patient generates the effort (chest expansion, shifts in bloodvolume, etc.) but does not achieve the desired effects that accompanygas exchange.

There are a variety of ventilation monitors such as 1) airway flowmetersand 2) capnometers (carbon dioxide analyzers). These monitors are usedroutinely for patients undergoing general anesthesia. These types ofmonitors work well when the patient's airway is “closed” in an airwaysystem such as when the patient has a sealing face mask or has theairway sealed with a tracheal tube placed into the lungs. However, thesesystems work less well with an “open” airway such as when nasal cannulaeare applied for oxygen supplementation. Thus, when a patient has anon-sealed airway, the options for tidal volume monitoring are limited.With an open airway, there have been attempts to monitor ventilationusing capnometry, impedance plethysmography, humidity, heat, sound andrespiratory rate derived from the pulse oximeter's plethysmogram. Someof the limitations are discussed below.

Nasal capnometry is the technique of placing a sampling tube into one ofthe nostrils and continuously analyzing the carbon dioxide contentpresent in the gas stream thereof. Nasal capnometry is relativelyeffective provided that 1) the patient always breathes through his/hernose, and 2) nasal oxygen is not applied. More specifically, if thepatient is talking, most of the exhalation is via the mouth, andfrequent false positive alarms sound because the capnometer interpretsthe absence of carbon dioxide in the nose as apnea, when in fact, it ismerely evidence of talking. Some devices in the prior art have tried toovercome this problem by: manual control of sampling from the nose ormouth (Nazorcap); supplementing oxygen outside of the nose whilesampling for CO₂ up inside the nose (BCI); providing oxygen in the nosewhile sampling CO₂ from the mouth (BCI); and supplying oxygen up onenostril and sampling for CO₂ up inside the other nostril (Salter Labs).None of these already-existing systems provide oxygen to both the noseand mouth or allow automatic control of sampling from either site oraccount for the possibility that one nostril may be completely orpartially obstructed compared to the other one. Further, if nasal oxygenis applied to the patient, the carbon dioxide in each exhalation can bediluted significantly by the oxygen supply. In this case, the capnometermay interpret the diluted CO₂ sample as apnea (stoppage in breathing),resulting once again, in frequent false positive alarms. Dilution of CO₂may also mask hypoventilation (detected by high CO₂) by making a highCO₂ value appear artifactually normal and thus lull the clinician into afalse sense of security, that all is well with the patient.

Impedance plethysmography and plethysmogram respiratory rate countingalso suffer drawbacks as primary respiratory monitors. Both devicesmeasure the “effort” of the patient (chest expansion, shifts in bloodvolume). Impedance plethysmography is done via the application of asmall voltage across two ECG electrode pads placed on each side of thethoracic cage. In theory, each respiration could be detected as thephasic change of thoracic impedance. Unfortunately, the resulting signaloften has too much noise/artifact which can adversely affectreliability. Respiratory rate derived from the pulse oximeter'splethysmogram may not diagnose apnea and distinguish it from completeairway obstruction, thus misdiagnosing apnea as a normal condition (afalse negative alarm state).

The arterial concentration of an inhalational or intravenous drug or gasis clinically useful and may be inferred from the end-tidalconcentration of the drug or gas measured in the gases exhaled by thepatient. The end-tidal concentration of a desired component of theexhaled gas mixture can be monitored and used to infer the arterialconcentration. Examples of drugs and gases that can be monitoredinclude, among other things: propofol, xenon, intravenous anestheticsand sedatives, and water vapor.

Various inspired gas compositions may be administered to patients fordifferent purposes. Oxygen diluted with air may be used instead of pureO₂ to reduce the risk of an oxygen-enriched micro-environment that maysupport or promote ignition of a fire, especially for those proceduresusing lasers (such as laser resurfacing of the face). An oxygen-heliummixture may be used to reduce the resistance to flow. Anoxygen/air/bronchodilator mixture may be used to treatbronchoconstriction, bronchospasm or chronic obstructive pulmonarydisease (COPD). A mixture of O₂ and water vapor may be used to humidifyand loosen pulmonary secretions.

In view of the above drawbacks to current systems for deliveringinspired gas and gas sampling, including monitoring ventilation, thereis a need for an improved combined system to accomplish these functions.

SUMMARY OF THE INVENTION

One of the purposes of the current invention is to increase the alveolarconcentration of an inspired gas, such as oxygen, without therequirement for a patient to wear a face mask. This is done by, amongother things: a) determining the patient's breath phase, namely whetherthe person is in the inhalation or exhalation phase of their respiratorycycle; and b) delivering a higher flow of inspired gas during theinhalation part of the respiratory cycle thereby making this higher flowof inspired gas acceptable to patients. In one aspect of the inventionthe inspired gas flow may be provided to all three respiratory orifices(i.e., both nostrils and the mouth) or directly in front of the mouth,during the inhalation cycle. Thus, dilution of inhaled gas by room airat an inhalation portal is reduced.

A second purpose of the invention is to more effectively sample exhaledgases, such sampling could be used, for example, to monitor patientventilation, in combination with mask-free delivery of inspired gas tothe patient. In this aspect, the invention includes placing pressurelumens and gas-sampling lumens inside, or near, at least one of apatient's nostrils and, in some embodiments, the mouth. The pressurelumens are connected to pressure transducers that in turn are connectedto a controller or processor running custom software algorithms fordetermining breath phase (inhalation or exhalation) and rate. Thepressure samples from the respective lumens are compared with oneanother to determine the primary ventilatory path. The gas samplingtubes may be connected to gas analyzers or monitors, e.g., CO₂analyzers, that measure the level of a gas or drug in the exhaled gas.

Other aspects of the invention will be apparent from the descriptionbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side, cut out view of the disposable portion of theapparatus placed on a patient in accordance with one embodiment of theinvention.

FIG. 2 shows a perspective exterior view of the disposable portion ofthe apparatus in accordance with one embodiment of the invention.

FIG. 3 is a blow-up view showing the lower, middle and cover portions ofthe disposable portion of the apparatus in accordance with oneembodiment of the invention.

FIG. 4 shows an embodiment of the disposable portion of the apparatuswith an oral collection chamber in accord with one embodiment of theinvention.

FIG. 5A is a schematic diagram of a gas delivery and gas sampling systemin accordance with one embodiment of the invention.

FIG. 5B is a schematic diagram of a gas delivery and gas sampling systemin accordance with an alternative embodiment of the invention:

FIG. 6 is a schematic diagram of pressure transducer circuitry in oneembodiment of the invention.

FIG. 7 is a diagram of a pressure waveform during a respiration cycleused in one method of the invention.

FIG. 8 is a flow chart of a preferred embodiment of one method of theinvention.

FIG. 9 is a schematic diagram of a gas delivery and gas sampling systemin accordance with an alternative embodiment of the invention.

FIG. 10 is a perspective diagram of an alternative embodiment of anoronasal gas diffuser and gas sampling device in accord with theinvention.

FIG. 11 is a side-elevation frontal view of the device shown in FIG. 10.

FIG. 12 is a plan view of the bottom of the device shown in FIG. 10.

FIG. 13 is a side-elevation back view of the device shown in FIG. 10.

FIG. 14 is a cross-sectional view of the tubing that connects the devicein FIG. 10 to the circuitry in FIG. 9.

FIG. 15 is a view of a connector that interfaces the machine end of theextruded tubing of FIG. 14 to a medical device.

DESCRIPTION OF PREFERRED EMBODIMENTS

Single Capnometer Embodiment

The concept of the invention will now be described using, merely by wayof example, supplemental oxygen as the inspired gas mixture and gassampling of carbon dioxide in the patient's exhalations. It should beunderstood that the concept of the invention is not limited tosupplemental O₂ administration and CO₂ sampling.

FIG. 1 shows a cut-out view of the disposable portion 4 of an apparatusin accordance with the invention placed on a patient 10.

The apparatus provides for the mask-free delivery of supplemental oxygengas to the patient combined with the monitoring of patient ventilation.Oxygen gas is supplied to the patient from an O₂ supply tube 12 andexits portion 4 from a diffuser grid 14 in housing 16 (shown in moredetail in FIG. 2). Diffuser grid 14 blows diffused oxygen into theimmediate area of the patient's nose and mouth. Two thin lumens (tubes)are mounted adjacent one another to portion 4 and placed in one of thepatient's nostrils (nasal lumens 18). Another two thin lumens are alsomounted adjacent to one another to portion 4 and placed in front of thepatient's mouth (oral lumens 20).

Of nasal lumens 18, one lumen is a pressure lumen for sampling thepressure resulting from a patient's nose breathing and the other lumencontinuously samples the respiratory gases so they may be analyzed in acapnometer to determine the concentration of carbon dioxide. Thisarrangement is essentially the same for oral lumens 20, namely, onelumen is a pressure lumen (samples pressure in mouth breathing) and theother lumen continuously samples the respiratory gases involved in mouthbreathing.

Nasal lumens 18 and oral lumens 20 are each connected to their ownpneumatic tubes, e.g., 22, which feed back the nasal and oral pressuresamples to pressure transducers (not shown) and which feed back thenasal and oral gas samples to a capnometer (not shown). All of portion4; lumens 18, 20; oxygen supply tubing 12 and feedback tubing 22 aredisposable (designed to be discarded, e.g., after every patient use),and preferably constructed of pliable plastic material such as extrudedpolyvinyl chloride.

As shown in FIG. 2, lumens 18, 20 and tubings 12 and 22, although shownas a portion cut-out in FIG. 1 in a preferred embodiment, are housed incover 30. Also, in FIG. 2, nasal lumens 18 (including pressure lumen 28and gas sampling lumen 26) are preferably formed from a double-holed,single-barrel piece. Oral lumens 20 (which include pressure lumen 32 andgas sampling lumen 34) are preferably formed from a double barrel piece.Diffuser grid 36 is formed in cover 30 and functions as an oxygendiffuser which releases a cloud of oxygen into the immediate oral andnasal area of the patient 10.

FIG. 3 shows a disposable portion 4 including cover 130 in more detailin cut-out fashion. Specifically, lower portion 110, formed from asuitably firm, but not rigid; plastic, has an opening 112 for insertionof oxygen supply tube 12. Slot 114 in portion 110 receives the oxygengas from the tube 12, retains it, and forces it up through opening 148in middle portion 112. Middle portion 112 is affixed to lower portion110 lying flat on portion 110. From opening 148, the oxygen gas travelsinto cover 130 (affixed directly onto middle portion 112) and travelslengthwise within cover 130 to the diffuser portion, whereupon theoxygen exits cover 130 through diffuser grid 136 into the immediatevicinity of the patient's nose and mouth in a cloud-like fashion. It ispreferable to supply oxygen flow to all three respiratory orifices (bothnostrils and mouth) to increase the concentration of oxygen provided tothe patient. By providing flow to all three orifices, dilution ofinhaled gas at an inhalation portal by pure room air is reduced. Also, adiffused stream such as that created by grid 136 is a preferredembodiment for the oxygen stream delivered to the patient. This isbecause a stream of oxygen delivered through a single lumen cannula istypically uncomfortable at high flow rates necessary for sufficientoxygen delivery. Further, at these flow rates, a single lumen can createan undesirable Bernoulli effect. It is noted that an alternative to thediffuser grid 136 is a cup-shaped or other chamber which receives the O2jet stream and includes a foam or filler paper section for diffusing thejet stream of O2.

As is also shown in FIG. 3, feedback tubing 22 enters lower portion 110at openings 122. At opening 122 begin grooves 146 and 140 formed inlower portion 110 each for receiving the feedback pressure sample fromlumens 128 and 132. At opening 122 begin grooves 144 and 142, formed inlower portion 110 each for receiving the feedback CO₂ sample from lumens126 and 134. Grooves 146, 144, 140 and 142, all formed in lower portion110, connect at one end to their respective sampling lumens (128, 126,132 and 134) and at their other end to feedback tubing 22; middleportion 112 lies flat on and affixed to portion 110 such that thegrooves 146, 144, 140 and 142 form passageways for the respectivefeedback samples. As can be seen, when assembled, portions 130, 112 and110 together form whole disposable piece 4, shown perspectively in FIG.2.

FIG. 4 shows a preferred embodiment of disposable portion 4 (hereportions 110 and 112 are shown affixed to one another) with an oralsample collection chamber 210 fitting over oral lumens 220 (nasal lumensare shown at 218 and the opening for the oxygen supply tube is shown at212). Oral sample collector 210 is preferably constructed of plastic andcreates a space in chamber 214 that collects a small volume of gas thepatient has breathed orally. That volume of gas is then sampled bylumens 220 and fed back for analysis through the respective pressure andCO₂ feedback tubing to pressure transducers and the capnometer describedabove. Collector 210 thus acts as a storage container for bettersampling of the oral site. It also serves as a capacitor for bettermonitoring of oral site pressure (exhalation contributes to volume andpressure increases, while inhalation removes gas molecules from volume214 and pressure decreases).

In one preferred embodiment, collector 210 is provided in a variety ofsizes and shapes to collect different volumes of air or to facilitatedifferent medical procedures which may be performed in or near themouth. In another preferred embodiment collector 210 is adjustable inthat it is capable of sliding over lumens 220 to enable positioningdirectly over the mouth's gas stream. In a further embodiment, lumens220 are themselves also slidably mounted to portion 222 so as to beextendable and retractable to enable positioning of both the lumens andcollector directly in front of the oral gas stream.

The present invention generally provides that in the event that positivepressure ventilation has to be applied via face mask, it should bepossible to leave the apparatus of the invention in place on the personto minimize user actions during an emergency. Thus, the apparatus of theinvention allows a face mask to be placed over it without creating asignificant leak in the pillow seal of the face mask. The material ofthe apparatus in contact with the face is preferably soft (e.g.,plasticized PVC, etc.) and deformable. This prevents nerve injury, oneof the most common complications of anesthesia, which is often caused bymechanical compression or hyperextension that restricts or shuts off theblood supply to nerves.

FIG. 5A shows a schematic circuit diagram of a preferred embodiment ofthe oxygen delivery and gas sampling system of the invention. Asdescribed above, disposable portion 304 includes nasal lumens whichsample a nasal (nares) volume 318 of gas breathed through the patient'snostril; an oral sample collector which creates an oral volume of gas320 effecting sampling of gas breathed through a patient's mouth; and anoxygen diffuser 336 which enriches the immediate breathing area of apatient with oxygen, increasing the patient's fraction of inspiredoxygen and thereby increasing the patient's alveolar oxygen levels. Thediffuser 336 ensures that a high rate of oxygen flow is notuncomfortable for the patient.

Oxygen gas is supplied to diffuser 336 from an oxygen supply (O₂ tank orin-house oxygen). If the supply of O₂ is from an in-house wall source,DISS fitting 340 is employed. The DISS fitting 340 (male body adaptor)has a diameter indexed to only accept a Compressed Gas Associationstandard oxygen female nut and nipple fitting. A source pressuretransducer 342 monitors the oxygen source pressure and allows customsoftware running on a processor (not shown) to adjust the analog inputsignal sent to proportional valve 346 in order to maintain auser-selected flow rate as source pressure fluctuates. Pressure reliefvalve 348 relieves pressure to the atmosphere if the source pressureexceeds 75 psig. Proportional valve 346 sets the flow rate of oxygen(e.g., 2.0 to 15.0 liters per minute) through an analog signal andassociated driver circuitry (such circuitry is essentially a voltage tocurrent converter which takes the analog signal to a dictated current tobe applied to the valve 346, essentially changing the input signal tothe valve in proportion to the source pressure, as indicated above). Itis noted that flowrates of 2.0 and 15.0 L/min could also be accomplishedby 2 less expensive on/off valves coupled with calibrated flow orificesinstead of one expensive proportional flow control valve. Downstreampressure transducer 350 monitors the functionality of proportional valve346. Associated software running on a processor (not shown) indicates anerror in the delivery system if source pressure is present, the valve isactivated, but no downstream pressure is sensed. As described above, thenares volume 318 and oral collection volume 320 are fed back to thecapnometer 352 via a three-way valve 354. The capnometer 352 receivesthe patient airway gas sample and monitors the CO₂ content within thegas sample. Software associated with capnometer 352 displays pertinentparameters (such as a continuous carbon dioxide graphic display known asa capnogram and digital values for end-tidal CO₂ and respiration rate)to the user. A suitable capnometer may be that manufactured by NihonKohden (Sj512) or CardioPulmonary Technologies (CO₂WFA OEM). Three-wayvalve 354 automatically switches the sample site between the oral siteand the nasal site depending on which site the patient is primarilybreathing through. This method is described in more detail below, butbriefly, associated software running on a processor (not shown) switchesthe sample site based on logic that determines if the patient isbreathing through the nose or mouth. It is preferable to have a shortdistance between the capnometer and valve 354 to minimize dead spaceinvolved with switching gas sample sites.

Also as described above, the nares volume 318 collected is fed back to anasal pressure transducer 356 and nasal microphone 358. Transducer 356(such as a Honeywell DCXL01DN, for example) monitors the pressure in thenares volume 318 through the small bore tubing described above.Associated software running on a processor (not shown) determinesthrough transducer 356 if the patient is breathing primarily through thenose. Associated offset, gain and temperature compensation circuitry(described below) ensures signal quality. Nasal microphone 358 monitorsthe patient's breath sounds detected at the nasal sample site.Associated software allows the user to project sound to the room andcontrol audio volume. Output from nasal microphone 358 may be summedwith output of the oral microphone 360 for a total breath sound signal.In an additional embodiment the breath sound signals are displayed tothe user and/or further processed and analyzed in monitoring thepatient's physiological condition.

Oral pressure transducer 362 (such as a Honeywell DCXL01DN, for example)monitors pressure at the oral collection volume 320 through the smallbore tubing described above. Associated software running on a processor(not shown) determines via pressure transducer 362 if the patient isprimarily breathing through the mouth. Offset gain and temperaturecompensation circuitry ensure signal quality. Oral microphone 360operates as nasal microphone 358 described above that amplifies andprojects breath sounds to the room. Alternatively, a white noisegenerator reproduces a respiratory sound proportional to the amplitudeof the respiratory pressure and encoded with a sound (WAV file) of adifferent character for inhalation versus exhalation so that they may beheard and distinguished by a care giver in the room.

A dual chamber water trap 364 guards against corruption of the CO₂sensors by removing water from the sampled gases. Segregated chamberscollect water removed by hydrophobic filters associated with the nasaland oral sites. This segregation ensures that the breathing siteselected as the primary site is the only site sampled. The disposableelement 304 is interfaced to the non-disposable elements via a single,multi-lumen connector 344 that establishes five flow channels in asingle action, when it is snapped to the medical device containing thenon-disposable equipment.

FIG. 5B shows an additional embodiment of the system circuit of thepresent invention, including a gas sample bypass circuit which keeps thegas sample at the oral and nasal sites flowing at the same rate,regardless of whether the site is being sampled by the capnometer orbypassed. Specifically, nasal diverter valve 555 switches the nasal gassample site between the capnometer and the bypass line. Activation ofthe valve 555 is linked to activation of oral diverter valve 557 inorder to ensure that one sample site is connected to the bypass linewhile the other sample site is connected to the capnometer. This allowstwo states: 1) the oral gas sample site fed back to the capnometer, withthe nasal gas sample site connected to the bypass; and 2) the nasal gassample site fed back to the capnometer with the oral gas sample site onbypass. As described above, the control software switches the gas samplesite based on logic that determines if the patient is breathing throughthe nose or mouth. Oral diverter valve 557 switches the oral gas samplesite between the capnometer and the bypass line and operates asdescribed with respect to nasal diverter valve 555.

Bypass pump 559 maintains flow in the bypass line 561 that is equivalentto flow dictated by the capnometer (e.g., 200 cc/min.). The pump 559also ensures that the gas sample sites are synchronized with one anotherso that the CO₂ waveform and respiration rate calculations are notcorrupted when gas sample sites are switched. Flow sensor 563 measuresthe flow rate obtained through the bypass line 561 and provides same toelectronic controller 565 necessary for flow control. Controller 565controls the flow of pump 559.

As can be seen from FIG. 5B, balancing the flow between the active gassample line and the bypass line (e.g., maintaining a flow in the bypassequivalent or near equivalent to the flow within the CO₂ sampling line,e.g., 200 cc/min) is desired. This prevents corruption of the CO₂waveform and respiration rate calculations in the event one site becameoccluded such that the bypass and capnometer lines flowed at differentrates.

FIG. 6 shows a schematic of the electronic circuitry associated withpressure transducers 356 and 362. Such circuitry includes a pressuresensor 402, a hi-gain amplifier 404, a temperature compensation andzeroing circuit 406 and a low pass filter 408. The gain and temperaturezeroing circuit ensure signal quality for the pressure transduceroutput. Depending on the signal to noise ratio of the pressuretransducer 402, the low pass filter 408 may be optional.

FIG. 7 is a diagram of the pressure reading (oral or nasal) during atypical respiration cycle with thresholds A, B, C and D identified inaccordance with the preferred method of the invention. As is shown, asexhalation 706 begins, the pressure becomes positive, eventuallyreaching a peak then dropping back to zero (atmospheric pressure) as theexhalation completes. The beginning of inhalation 708 is indicated bythe pressure becoming negative (sub-atmospheric). The pressure willbecome more negative during the first portion of inhalation then trendback towards zero as inhalation ends.

The control software of the present invention defines an upper and alower threshold value 702, 704, respectively. Both are slightly belowzero, with the lower threshold 704 being more negative than the upperthreshold 702. During each respiration cycle the software determineswhen the thresholds 702, 704 are crossed (points A, B, C, and D, FIG. 7)by comparing the pressures to one of the two thresholds. The crossingsare expected to occur in sequence, i.e., first A, then B followed by C,and finally D. An O₂ source valve is turned up (e.g., to 10-15liters/min of flow) when point A, 710, is reached and turned down (e.g.,to 2-3 liters/min of flow) when C, 712, is reached, thus providing thehigher oxygen flow during the majority of the inhalation phase.

To determine when the threshold crossings occur, the software examinesthe pressures from the oral and nasal pressure sensors at periodicintervals, e.g., at 50 milliseconds (see FIG. 8, step 820). During eachexamination, the software combines the oral and nasal pressures and thencompares the combined pressure to one of the two thresholds as follows.

As shown by the flowchart of FIG. 8, when the software begins execution,it reads the nasal and oral pressures, step 802, and awaits a combinedpressure value less than the upper threshold (point A), step 804. Whenthis condition is met, the software turns up the O₂ valve, step 806, toa higher desired flow (e.g., 10-15 liters/min) then begins looking for acombined pressure value less than the lower threshold (point B), step808. When this occurs the software waits for a combined pressure valuethat is greater than the lower threshold (point C). When this value isread, the O₂ is turned down to the lower desired flow rate (e.g., 2-3liters/min), step 810, and the software awaits a pressure value thatexceeds the upper threshold (point D). Once this value is read, thecycle begins again for the next breath. In the case of oxygen, theinvention may thus increase end tidal oxygen concentrations from thebaseline 15% (breathing room air) up to 50-55%. Whereas this may not beas effective as face mask oxygen supplementation, it is significantlybetter than the prior art for open airway oxygen supplementationdevices.

Also, instead of completely shutting off inspired gas flow duringexhalation, the invention selects a baseline lower flow of inspired gas,e.g., 2 L/min, so that the flow interferes minimally with the accuracyof exhaled gas sampling. The non-zero inspired gas flow duringexhalation enriches the ambient air around the nose and mouth that isdrawn into the lungs in the subsequent inhalation. Further, in the eventthat O₂ is the inspired gas and that the software malfunctions such thatthe algorithm stays stuck in the exhalation mode, a non-zero baselineflow of O₂ will ensure that the patient breathes partially O₂-enrichedroom air rather than only room air.

As described above, a capnometer may be used to provide information suchas end-tidal CO₂ and respiration rate by continually sampling the levelof CO₂ at a single site. Since breathing can occur through the nose,mouth, or both, the software must activate valve 354 (FIG. 5A) or valves555 and 557 (FIG. 5B), that switch the capnometer-sampling site to thesource providing the best sample, i.e., mouth or nose.

As is also shown in FIG. 8, the software determines the best samplingsite by examining the oral and nasal pressure readings at periodicintervals. During each examination, the current and prior three oralpressure values are compared to the corresponding nasal pressure values.If the combined nasal pressures exceed the combined oral pressures bymore than a factor of three, the capnometer sample is obtained at thenose. If the combined oral pressures exceed the combined nasal pressuresby more than a factor of three, the sampling occurs at the mouth.

It is further noted that the gas sampling lumens may be connectedtogether at a switching valve to minimize the number of gas analyzersrequired. Via the switching valve, the gas sampling lumen connected tothe primary ventilatory path is routed to the gas analyzer.Additionally, in some aspects of the invention, the user sees a displayfrom one gas analyzer. For example, for a capnometry application, theCO₂ tracing that has the highest averaged value (area under the curveover the last n seconds, e.g., 15 seconds) is displayed. Because thepresent invention measures the “effect,” i.e., the CO₂ and airwaypressure variations with each breath, it would not fail to detect acomplete airway obstruction.

Multiple Capnometer Embodiment

An alternative embodiment of the invention uses two capnometers as shownin FIGS. 9, 912 and 914. Pressure transducer 906 monitors the pressureat nose tap 938. Pressure transducer 908 monitors the pressure at nosetap 940. Each nose tap 938 and 940 samples the pressure in one of thepatient's nares. Pressure transducers 906 and 908 can be momentarilyconnected to atmosphere for zeroing purposes via valves 904 and 902respectively. Pressure is not monitored at the mouth. The primary nasalventilatory path is determined from analysis of the pressure trace ateach nares. The nare whose pressure trace exhibits the larger amplitudeof pressure oscillation is considered to be the primary nasalventilatory path.

Gas sample lumens are placed at both nares and at the mouth. The oralgas sample lumen 932 is directly connected to the oral capnometer 914.The nasal capnometer 912 can be connected to either of the nasal gassampling lumens 934 or 936 via a switching valve 910. Once the pressuretransducers and the software determine the primary nasal ventilatorypath, the switching valve routes the gas sample from the primary nasalventilatory path to the nasal capnometer 912. Thus, exhaled gas issampled continuously from either the right or left nasal passage.

The software analyzes the sum of the pressures sampled from the twonasal orifices to determine whether the patient is inhaling or exhaling.Obviously, different algorithms may be possible like determining thebreath phase from only the pressure trace at the primary nasalventilatory path, instead of adding the pressures from both nares.Software running on a processor (not shown) opens a valve 922 connectedto an oxygen source so that oxygen flow to the patient through outlet930 is high (e.g. 15 L/min) during the inhalation phase of the patient'sbreathing. A high pressure relief valve 918 relieves pressure if the O₂supply pressure exceeds 75 psig. A pressure transducer 920 monitors theO₂ supply pressure such that the software can adjust the opening of thevalve 922 to compensate for O₂ supply pressure fluctuations. A pressurerelief valve 924 downstream of the valve 922 prevents pressure buildupon the delivery side. Components 918, 920, 922 and 924 are mounted on agas manifold 916 with internal flow passages (not shown) to minimize thenumber of pneumatic connections that have to be manually performed.

An audio stimulus through outlet 928 generated by subsystem926 is usedto prompt the patient to perform a specific action like pressing abutton as a means of assessing responsiveness to commands as an indirectmeasure of patient consciousness. This automated responsiveness test isuseful in a conscious sedation system like, for example, that describedin U.S. patent application Ser. No. 09/324,759 filed Jun. 3, 1999, nowU.S. Pat. No. 6,807,965.

The oronasal piece 1000 in FIG. 10 is intended for use with the circuitin FIG. 9. A pressure sampling lumen 1008 and a gas sampling lumen 1006are contained within left nostril insert 1004 that fits into the leftnare of the patient. A pressure sampling lumen 1058 and a gas samplinglumen 1056 are contained within right nostril insert 1054 that fits intothe right nare of the patient. A multiplicity of holes 1012 diffuse O₂near the region of the nares. A similar multiplicity of holes 1026 (FIG.12) diffuse O₂ near the region of the mouth, to account for thepossibility of mouth breathing. The oronasal piece 1000 is held onto thepatient's face via an adjustable loop of cord or elastic band 1014 thatis designed to be rapidly adjusted to the patient. A single cord orelastic band is made to form a loop by passing both cut ends via anadjustment bead 1018. The loop is attached in one motion to bayonet-typenotches 1020 on oronasal piece 1000 that securely hold the cord in placeon the oronasal piece while it is being wrapped around the back of thepatient's head. The adjustment bead 1018 is then slid along the loop toadjust the tension on the cord. Once adjusted, the loop is then releasedover the stud 1016 such that the stud tends to splay the two pieces ofcord apart, thus locking the adjustment bead to prevent inadvertentloosening of the adjustment bead. The gas sample lumen 1024 (FIG. 11) iscontained within protuberance 1022 which is designed to stick out intothe stream of gas flowing to and from the mouth.

Referring now to FIG. 13, lumen 1038 on the oronasal piece 1000 isinternally connected to the gas sample lumen 1006 (FIG. 10) for the leftnare. Lumen 1036 (FIG. 13) on the oronasal piece 1000 is internallyconnected to the oral gas sample lumen 1024 (FIG. 11). Lumen 1034 (FIG.13) on the oronasal piece 1000 is internally connected to the pressuresampling lumen 1008 (FIG. 10) for the left nare. Lumen 1030 (FIG. 13) onthe oronasal piece 1000 is internally connected to the gas sample lumen1056 (FIG. 10) for the right nare. Lumen 1028 (FIG. 13) on the oronasalpiece 1000 is internally connected to the multiplicity of holes 1012 and1026 (FIGS. 10 and 12) that allow O₂ to diffuse into the regions closeto the nose and mouth. Lumen 1032 (FIG. 13) on the oronasal piece 1000is internally connected to the pressure sampling lumen 1058 (FIG. 10)for the right nare. The details of the internal flow passages inoronasal piece 1000 to accomplish the above connections will be evidentto one skilled in the art.

Referring to FIG. 14, the oronasal piece 1000 of FIG. 10 is connected tothe circuit of FIG. 9 via the extruded tear-apart tubing of FIG. 14. Theextruded tubing contains seven lumens grouped in three clusters (1142,1144 and 1146) that can be separated from each other by manually tearingalong the tear lines 1143 and 1145. Lumen 1130 in cluster 1142 channelsthe flow of O₂ to the oronasal piece and is of larger bore toaccommodate the high flow of O₂ and present minimal flow resistance.Lumen 1128 in cluster 1146 carries the audio stimulus that prompts thepatient to squeeze a button as part of an automated responsiveness test(ART) system. Lumen 1132 in the middle of cluster 1144 carries the oralgas sample. Lumens 1138 and 1134 in cluster 1142 carry the pressure andgas samples from one nasal insert. Lumens 1140 and 1136 in cluster 1144carry the pressure and gas samples from the other nasal insert. Thecross-section of each cluster is shaped like an aerofoil to adapt to theindentation of the facemask pillow seal and the cheek of the patientwhen a facemask is placed over the separated clusters. The lumens arearranged such that the larger bore lumens are in the middle of eachcluster, taking advantage of the aerofoil like cross-section of eachcluster.

An additional feature of the invention is that the pneumatic harness(shown in cross-section in FIG. 14) can be connected to a standard,male, medical O₂ barbed outlet connector commonly referred to as a“Christmas tree,” so that the oronasal piece of the invention can alsobe used post-procedurally to deliver O₂-enriched air to the patient.Another feature of the invention is that the pneumatic harness of FIG.14 can be snapped onto a medical device with a single action. Toaccomplish both design objectives, the connector of FIG. 15 is used toadapt the pneumatic harness of FIG. 14 for connection to a medicaldevice. The pneumatic harness of FIG. 14 is mounted onto adapter 1148using seven male ports like ports 1150 and 1152. Port 1152 carries theoxygen inflow and port 1150 pipes in the audio stimulus. The adapter1148 has a tapered inlet connected to the O₂ delivery lumen 1130 (FIG.14). The tapered inlet is made of soft material and is designed to mateto a standard male O₂ barbed connector known as a Christmas tree. Theconnector snaps into a socket on the medical device to establish sevenairtight pneumatic connections with only one action. Tapered male port1158 on the medical device delivers oxygen into lumen 1130 via port1152. Port 1156 brings in the pressure signal from nose pressure tap 2.Pegs 1154 allow the multi-lumen connector 1148 to be held in tightly andsecurely once snapped into the medical device to prevent accidentaldisconnection.

The above-described systems and methods thus provide improved deliveryof inspired gas and gas sampling, including CO₂ sampling, without use ofa face mask. The system and method may be particularly useful in medicalenvironments where patients are conscious (thus comfort is a realfactor) yet may be acutely ill, such as in hospital laboratoriesundergoing painful medical procedures, but also in the ICU, CCU, inambulances or at home for patient-controlled analgesia, among others. Itshould be understood that the above describes only preferred embodimentsof the invention. It should also be understood that while the preferredembodiments discuss gas sampling, such as CO₂ sampling and analysis, theconcept of the invention includes sampling and analysis of other medicalgases and vapors like propofol, oxygen, xenon and intravenousanesthetics. It should further be understood that although the preferredembodiments discussed address supplemental O₂ delivery, the concept ofthe invention is applicable to delivery of pure gases or mixtures ofgases such as O₂/helium, O₂/air, and others.

1. An improved mask-free delivery apparatus that delivers inspired gasto a patient and accurately samples expired gases from the patient, saidapparatus comprising: an inspired gas delivery device having a bodycomprising nasal lumens for extending into the patient's nares, saidnasal lumens receiving patient exhalations and delivering same to apressure analyzer for determining the phase of the patient's respiratorycycle and to a gas analyzer for analyzing the exhalation, and an orallumen extending downward from the base for receiving patient exhalationsfor delivering same to a gas analyzer for analyzing the exhalation, saidinspired gas delivery device having diffuser outlets carried by saidbody and being connected to a controller that modulates the flow ofinspired gas to the patient in accordance with the phase of thepatient's respiratory cycle, said outlets being spaced apart from theopening of said lumens to minimize dilution of said gas sample, apressure analyzer being connected to said nasal lumens for determiningthe phase of the patient's respiratory cycle, and at least one gasanalyzer being connected to said nasal lumens and said oral lumens, thesaid at least one gas analyzer measuring the level of a gas or drug inthe exhaled gas, said pressure analyzer being connected to saidcontroller for increasing the delivery of gas during the inhalationphase of the patient's respiratory cycle and for reducing the deliveryof gas during the exhalation phase of the patient's respiratory cycle.2. The apparatus of claim 1, wherein at least two of said nasal and orallumens are connected to a pressure comparator to determines thepatient's primary respiratory site.
 3. The apparatus of claim 1 in whichsaid device is provided with an audio stimulus to measure the patient'sconsciousness.
 4. The apparatus of claim 1, wherein said higher flow ofsupplied gas is delivered during a portion of the inhalation phase ofthe patient's respiratory cycle, and wherein said portion of theinhalation phase ends in advance of the exhalation phase.
 5. Theapparatus of claim 1 in which said diffuser outlets provides diffusedoxygen into the immediate area of the patient's nose and mouth.
 6. Theapparatus of claim 1, wherein said lumens and said inspired gas deliverydevice comprise a pneumatic harness, and wherein said lumens areprepackaged in one or more clusters, said clusters being manuallyseparable from one another and attachable to said elongated body priorto positioning on the patient.
 7. The apparatus of claim 1, wherein saidpressure analyzer monitors changes in the sum of the pressures detectedat both the nostrils.
 8. The apparatus of claim 1 in which each of saidnasal lumens are separated into a pressure lumens and a nasal lumens. 9.An improved mask-free device for delivering oxygen to a patient and forobtaining a more accurate sample of the patient's expired gas, saidapparatus comprising: a) a housing comprising a mask-free deliverydevice for delivering oxygen from a supply source to said patient in thearea of the patient's mouth and nose, said oxygen being deliveredthrough diffuser outlets carried by said housing; b) pressure samplingand gas sampling lumens extending from said housing for receiving saidpatient's respiratory exhalations and for transmitting same to apressure transducer for monitoring the pressure at the patient's naresand for transmitting same to a gas sampling analyzer for analyzing saidexhalation; d) a control processor interconnected to said pressuretransducer and said oxygen supply source for ascertaining the pressureof said patient's exhalations and for reducing the supply of oxygendelivered to said patient during the patient's exhalation to avoiddilution of said exhalation and to obtain a more accurate analysis ofsaid patient's exhalation.
 10. A device as recited in claim 9 in whichsaid control processor also increases the flow of oxygen during thepatient's exhalation.
 11. A device as recited in claim 9 in which saidgas analyzer is a capnograph for determining the patient's carbondioxide level.
 12. A device as recited in claim 9 in which said gasanalyzer is a capnograph for determining the level of the patient'scarbon dioxide exhalation.
 13. A device as recited in claim 9, whereinsaid higher flow of supplied gas is delivered during a portion of theinhalation phase of the patient's respiratory cycle, and wherein saidportion of the inhalation phase ends in advance of the exhalation phase.14. A device as recited in claim 9 in which said device is provided withan audio stimulus to measure the patient's consciousness.
 15. A deviceas recited in claim 9 in which said pressure sampling and said gassampling lumens extended into each comprise a single tubular element.16. A mask-free oronasal device for supplying oxygen to a patient andfor obtaining pressure and gas sampling from said patient, said devicecomprising: a generally flexible housing adapted to fit flat upon theupper lip of said patient; said housing having lumens extending upwardinto said patient's nares for collecting exhalations for transmittal topressure transducers and to a gas analyzer for monitoring the pressuregenerated by said patient during his inhalation and exhalations and forcapturing the patient's exhalations for analysis by said analyzer; saidhousing having a lumen extending downward for collecting exhalationsfrom the patient's mouth for transmittal to a gas analyzer formonitoring a gas generated by said patient during said exhalation; andconduits formed in said housing for delivering oxygen from a supply todiffuser openings in said housing adjacent said lumens from a supplysource to said patient; a control processor interconnected to saidpressure transducer and said oxygen supply source for controlling theflow of oxygen to said patient so as to increase said oxygen flow duringthe patient's inhalation and to decrease said flow during the patient'sexhalations and to minimize dilution of the collected exhalation to betransmitted to said analyzer.
 17. A device as recited in claim 16 inwhich said gas analyzer is a capnograph for determining the level ofcarbon dioxide exhaled by the patient.
 18. The device of claim 16,wherein said higher flow of supplied gas is delivered during a portionof the inhalation phase of the patient's respiratory cycle, and whereinsaid portion of the inhalation phase ends in advance of the exhalationphase.
 19. The device of claim 16 in which said pressure sampling andsaid gas sampling lumens extended into each nare comprise a singletubular element.